What was one of the primary contributions of Eratosthenes?

Eratosthenes is most famously known for his remarkable contribution to geography through the measurement of the Earth's circumference. He performed this feat in the 3rd century BCE by utilizing observations of the angles of the sun's rays at two different locations in Egypt—Syene (modern Aswan) and Alexandria. By knowing the distance between these two cities and the angle of the sun at each location during the summer solstice, he was able to calculate the Earth's circumference with remarkable accuracy for his time.

This contribution was not only significant because it demonstrated a sophisticated understanding of geometry and astronomy but also laid the foundation for future explorations and navigational techniques. Eratosthenes' work exemplifies the blending of mathematics and science in the ancient world, marking a pivotal moment in the history of geography and our understanding of the Earth.